1. Field of the Invention
The present invention relates to a linear actuator and method of operating the same for generating a reciprocating vibration, and more particularly relates to a vibrating linear actuator for use in a small appliance, e.g., a reciprocating electric shaver, or the like.
2. Description of the Related Art
A known vibrating linear actuator used for a reciprocating electric shaver is disclosed in Japanese unexamined patent publication No. 8-331826 and its counterpart, U.S. Pat. No. 5,736,797, which issued to Motohashi, et al. on Apr. 7, 1998. This known actuator includes a stator made of an electromagnet or a permanent magnet, and a moving portion that has or includes a permanent magnet or an electromagnet and is supported by a spring. This known vibrating linear actuator is supported by the spring, and the moving portion embodied as a spring vibration system can be vibrated at a natural frequency (i.e., a resonance frequency) of the spring vibration system. Thus, energy that is necessary for driving the system can be reduced. In addition, power supplied to a coil of the electromagnet can be controlled in accordance with an output of a detection system for detecting at least one of a displacement, a velocity and an acceleration of the moving portion, so that a vibration having a constant amplitude can be maintained despite a load variation.
However, though the above-mentioned feedback control is effective where a load variation is large, it is somewhat less than adequate when applied to devices having a small load variation in that it is more costly to use a feedback control system for a small fluctuating load. Since such feedback controls maintain the amplitude at a constant level by detecting every amplitude of the moving portion and by controlling the pulse width supplied to the coil of the electromagnet, costs associated with such feedback control are high.
Costs can be reduced by adding a fixed output quantity at a timing adapted to a predetermined frequency without using a feedback control system for making the amplitude constant. However, a vibration system including a spring has a varying natural frequency due to varying masses of manufactured individual springs (i.e., each spring used in each actuator can have a different mass based upon the manufacturing tolerances with respect to the mass of the spring). Therefore, when controlling the power supplied to a coil using a fixed frequency, the natural frequency does not match the control frequency, and the drive efficiency drops, resulting in a large power consumption and a condition where the vibration of the moving portion does not reach a predetermined amplitude. In addition, the life of the spring is shortened since the spring operates at a point away from the resonance point.
The present invention provides a vibrating linear actuator and method of operating the same, that increases drive efficiency without using an amplitude feedback control system. The actuator of the present invention includes a stator, a spring vibration system having both a moving portion having a magnet, and a spring configured to support the moving portion. The actuator further has an electromagnetic coil configured to receive an electrical current, whereupon the coil moves the moving portion against a load supplied by the spring to reciprocally move the moving portion. The actuator further includes a frequency detector configured to detect a natural frequency of the spring vibration system, and a frequency controller configured to determine a frequency of an electrical current pulse, the pulse to be received by the coil, in accordance with a detection result of the detector. Thus, the vibrating linear actuator of the present invention can vibrate the spring vibration system at its natural frequency without being affected by variation in the mass of the spring vibration system.
Additionally, the stator may include either an electromagnet or a permanent magnet, and similarly, the magnet of the moving portion may include either an electromagnet or a permanent magnet. The invention may further include an amplitude detector configured to detect a signal corresponding to an amplitude of the moving portion, and either or both of the frequency detector and the frequency controller is further configured to determine (i.e., set) a drive frequency by deriving the natural frequency from a variation of an amplitude value while incrementally altering the frequency of the current pulse to be supplied to the coil.
The drive frequency may be determined (i.e., set) when the amplitude value reaches its maximum or alternatively, can be determined when the amplitude value reaches a predetermined value or greater than the predetermined value.
In another embodiment, the actuator of present invention may further include a current value measuring device configured to measure a drive current supplied to the coil, and either or both of the frequency detector and frequency controller may be configured to determine a drive frequency by deriving the natural frequency from a variation of a drive current value while incrementally altering the frequency of the current pulse to be supplied to the coil.
The drive frequency may be a frequency when the drive current value reaches the minimum value or can be a frequency when the drive current value reaches or falls below a predetermined value.
The natural frequency may be determined under the condition that the current is not supplied to the coil. Preferably, the natural frequency may be determined at the end of the period while current is not supplied to the coil.
A pulse width of the drive current pulse can be decreased when the detected natural frequency is not within a predetermined range. In addition, current supply to the coil can be interrupted when the detected natural frequency is out of a predetermined range for a predetermined time or greater, so that needless power consumption can be avoided.
Furthermore, current supply to the coil can be interrupted when the detected natural frequency has not changed for a predetermined time, thereby preventing excess power consumption.
The method for vibrating a linear actuator includes, supplying the electromagnetic coil with electrical current, reciprocally moving the coil against a load supplied by the spring, in response to the supplying of current, detecting a natural frequency of the spring vibration system, determining a frequency of an electrical current pulse, in accordance with the detected natural frequency, and supplying the current pulse to the coil.
The method may further include sensing a signal corresponding to an amplitude of the moving portion, and determining a drive frequency by deriving the natural frequency from a variation of an amplitude value while incrementally altering the frequency of the current pulse to be supplied to the coil.
Additionally, the drive frequency may be determined when the amplitude value reaches a maximum value, or alternatively, when the amplitude value reaches or exceeds a predetermined value.
The method may also include measuring a drive current supplied to the coil, and determining a drive frequency by deriving the natural frequency from a variation of a drive current value while incrementally altering the frequency of the current pulse to be supplied to the coil.
Further, the drive frequency may be determined when the drive current value reaches a minimum value, or alternatively, when the drive current value reaches or falls below a predetermined value.
Also, the natural frequency may be determined while current is not being supplied to the coil, or alternatively, at the end of a predetermined period and while the current is not supplied to the coil.
The method may yet still further include decreasing a pulse width of the current pulse when the detected natural frequency is not within a predetermined range. The current supply to the coil may be interrupted when the detected natural frequency is out of the predetermined range for a predetermined time period, or alternatively, when the detected natural frequency remains unchanged for a predetermined time period.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.